The contest for the 2012 Republican presidential nomination has been described as a reality show and a circus. But what’s happening inside the GOP is quite rational and easily explained.

The obvious Republican nominee was Texas Gov. Rick Perry — obvious because his government-bashing, ideology-mongering, secessionist-flirting persona was a perfect fit for a Republican primary electorate that has shifted far to the right of Ronald Reagan.

E.J. Dionne writes about politics in a twice-weekly column and on the PostPartisan blog. He is also a senior fellow in Governance Studies at the Brookings Institution, a government professor at Georgetown University and a frequent commentator on politics for National Public Radio, ABC’s “This Week” and NBC’s “Meet the Press.” View Archive

The yearning for someone like Perry was inevitable. He combined the right views — actually, very right views — with experience as a chief executive that made him seem like somebody who was ready to be president.

Consider that even before he had gotten into the race, mere word that he might run sent Republican voters scrambling his way. He already had 18 percent to Romney’s 23 percent in a late July Gallup poll. Michele Bachmann was next at 13 percent. At that point, Newt Gingrich was at 6 percent and Herman Cain was at 4 percent.

After Perry announced his candidacy, he soared. The Aug. 17-21 Gallup survey had him at 29 percent, Romney at 17 percent, Bachmann down to 10 percent and Gingrich and Cain both at 4 percent. (Ron Paul, holding aloft the libertarian banner, holds his core voters no matter what’s happening around him. Paul was at 10 percent in July, 13 percent in August.) Another survey at the time by Public Policy Polling put Perry at 33 percent to 20 percent for Romney.

This nomination was Perry’s to lose, and lose it he appears to have done. This opened the way for the relatively short-lived, if entertaining, Herman Cain show, which finally closed on Saturday.

Yet Romney still can’t take off, and a lot of ink and online pixels have been spent trying to explain why. I see four factors holding Romney back. That he is a flip-flopper is no longer a charge by his opponents; it is taken as a given. His refusal to repudiate his Massachusetts health-care plan goes down badly with conservatives. His public personality is, well, stiff and patrician enough that the Internet is now full of videos of Romney’sawkwardness. And he is a Mormon, a problem for some conservative evangelicals.

It’s outrageous that Romney’s religion is an issue, and anyone analyzing its impact has a moral obligation to say so. Alas, that does not mean it has no effect. And Romney ought to be proud of his health initiative — although it’s disingenuous of him to deny the strong links between what he did and what President Obama fought to get enacted.

But what’s going on is not just a Romney problem. The Republican Party’s core electorate has changed radically since 2008 — and even then John McCain won the nomination against the wishes of many on the Republican right because the opposition to him was splintered.

A party that lived by the tea crowd in 2010 is being severely hobbled by it now. The Republican right wants the kind of purity that led it to take candidates such as Cain and Bachmann with great seriousness for a while. The same folks took Sharron Angle, Christine O’Donnell and Joe Miller seriously in the 2010 Senate primaries, too. None of them got elected.

Perry once seemed the answer to this problem. Now that he, Cain and Bachmann have faltered, lonely conservative hearts have turned to Gingrich. This is odd, since Gingrich can give Romney an excellent run in any flip-flopping contest.

But Gingrich has always kept at least one foot in the camp of movement conservatism, and he talks like a movement guy. This could be enough. The question is whether he has the discipline not to say something really foolish between now and Jan. 3, the date of the Iowa caucuses. (Free advice to Newt: Stop talking about yourself in the third person as a world historical figure.)

There is talk of the “Republican establishment” swooping in to save matters, and things certainly seem ripe for a draft write-in campaign for some new candidate. But the Republican establishment, such as it is, is essentially powerless. It sold its soul to the Tea Party, sat by silently as extremist rhetoric engulfed the GOP and figured that swing voters would eventually overlook all this to cast votes against a bad economy.

That’s still Romney’s bet; yet his failure to break through suggests the right wing will not be trifled with. Republican leaders unleashed forces that may eat their party alive. And the only Republican really enjoying what’s happening is Newt Gingrich.

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Comments our editors find particularly useful or relevant are displayed in Top Comments, as are comments by users with these badges: . Replies to those posts appear here, as well as posts by staff writers.